Bowlers like to practice with a new bowling ball to determine its performance attributes before purchasing the ball. This is especially true when the bowling ball is a new model and the rate of introduction of new models of bowling balls is accelerating. Bowlers' hands and thus their hand grips vary in size so usually a bowling ball is custom drilled for each purchaser. A bowling ball is usually shipped from the factory with a pair of finger holes predrilled to a standard diameter with each hole being 31/32" in diameter. Finger inserts of different diameters are then installed in these finger holes to match the finger size of the bowler. However, thumb holes are generally not predrilled because they can vary in their spacing across the surface of the bowling ball from the pair of finger holes over a range of 3" to 51/2". If a ball is drilled for a prospective purchaser and that purchaser decides, after trying the bowling ball on a bowling lane, not to purchase it, then the seller has a bowling ball in stock that cannot be custom drilled for another customer. In today's market, different types of bowling balls are being introduced at high rate. Customers would like to try each of the different models of bowling balls to determine which is best suited to the individual bowler's game. This normally require custom drilling of each model of each bowling ball for each customer which is prohibitively expensive.
Accordingly, this invention is directed to a method for drilling a small number of bowling balls for testing by a relatively large number of bowlers having hand spans of different sizes.
It is an object of this invention to provide a bowling ball having a predrilled set of standard finger holes and a predrilled thumb hole at a specified finger thumb span to be adaptable to use by other bowlers with the same finger thumb span but with different finger and thumb diameters.
It is another object of this invention to provide a relatively small number of bowling balls with thumb spans located at intervals of 1/8" in a span of 3" to 51/2" which balls can be adapted for use by most bowlers.
Yet another object of this invention is a simplified method of installing a removable thumb insert in a bowling ball.
Still another object of this invention is a method of drilling a thumb insert to a desired diameter while the thumb insert is installed in the bowling ball thumb hole.
A further object of this invention is a method of drilling a thumb insert in the form of a tube to a proper inside diameter when the tube is installed in the bowling ball thumb hole.
Yet an additional object of this invention is a method of locking a cylinder or tube in the thumb hole of a bowling ball to secure it against movement during drilling to a desired finger size.
Other objects of the invention will be found in the following specification, claims and drawings.